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GCN Circular 41755

Subject
Fermi GRB 250909A: Global MASTER-Net observations report
Event
GRB 250909A
Date
2025-09-09T02:45:32Z (4 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, 
G.Antipov,  A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-Tavrida robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 250909A ( Fermi GBM team, GCN 41753Loading...
 
 ) errorbox  31 sec after notice time and 68 sec after trigger time at 2025-09-09 02:34:37 UT, with upper limit up to  15.3 mag. Observations started at twilight.  The observations began at zenith distance = 17 deg. The sun  altitude  is -7.8 deg. 

The galactic latitude b =  1 deg., longitude l = 168 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2987637

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      74 | 2025-09-09 02:34:37 |      MASTER-Tavrida | (05h 35m 20.66s , +41d 15m 12.7s) |   C |    10 | 14.4 |        
      91 | 2025-09-09 02:34:50 |      MASTER-Tavrida | (05h 35m 20.96s , +41d 15m 12.4s) |   C |    20 | 15.1 |        
     124 | 2025-09-09 02:35:22 |      MASTER-Tavrida | (05h 23m 43.51s , +41d 45m 12.1s) |   C |    20 | 15.2 |        
     154 | 2025-09-09 02:35:22 |      MASTER-Tavrida | (05h 23m 43.50s , +41d 45m 12.1s) |   C |    80 | 15.3 |  Coadd 
     199 | 2025-09-09 02:35:22 |      MASTER-Tavrida | (05h 23m 43.51s , +41d 45m 12.2s) |   C |   170 | 15.3 |  Coadd 
     152 | 2025-09-09 02:35:45 |      MASTER-Tavrida | (05h 23m 43.26s , +41d 45m 11.6s) |   C |    30 | 15.0 |        
     184 | 2025-09-09 02:36:17 |      MASTER-Tavrida | (05h 23m 43.04s , +41d 45m 10.9s) |   C |    30 | 14.6 |        
     221 | 2025-09-09 02:36:50 |      MASTER-Tavrida | (05h 23m 42.76s , +41d 45m 10.4s) |   C |    40 | 15.1 |        
     276 | 2025-09-09 02:36:50 |      MASTER-Tavrida | (05h 23m 42.74s , +41d 45m 10.4s) |   C |   150 | 14.7 |  Coadd 
     269 | 2025-09-09 02:37:32 |      MASTER-Tavrida | (05h 23m 42.35s , +41d 45m 09.7s) |   C |    50 | 15.1 |        
     327 | 2025-09-09 02:38:25 |      MASTER-Tavrida | (05h 23m 41.85s , +41d 45m 08.4s) |   C |    60 | 14.7 |        
     395 | 2025-09-09 02:39:28 |      MASTER-Tavrida | (05h 23m 41.29s , +41d 45m 06.9s) |   C |    70 | 14.5 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.